"The merger will not result in any job losses for U.S.-based wireless call center employees of T-Mobile USA or AT&T," the companies wrote in a news release.

The text of the promise adds the caveat that the combined carriers won't eliminate jobs that exist "when the merger closes," leaving the door open for T-Mobile or AT&T to independently reduce call center employment prior to that time.

In a filing with the government pushing for the acceptance of the merger, AT&T wrote that it "expects that its customers will benefit from T-Mobile USA's industry-leading customer care practices."

"T-Mobile currently has over 600 employees in Chattanooga," said T-Mobile spokeswoman Anna Friedges. "Making this combination a success will require the talent and commitment of T-Mobile USA employees."

To underscore its commitment to U.S.-based call center workers, AT&T will also "bring back" 5,000 additional call center jobs to the U.S. that are currently outsourced if the deal is approved, and "significantly increase our investment here," said AT&T Chairman and CEO Randall Stephenson.

AT&T noted that it's jobs commitment "does not change its previous guidance on the expected overall merger synergies," which some analysts have estimated at up to $40 billion in savings from cutting duplicate positions and operations.

Yet the company's also estimates that a promised $8 billion in new investments following the proposed merger may create between 55,000 and 96,000 new jobs, according to a study commissioned by the Communications Workers of America labor union.

This stands in contrast to the billions in job cuts and other savings the company claims the merger will achieve, but AT&T clarified its position in an October letter to the FCC, saying "that although some jobs serving redundant functions would be eliminated to reduce costs, AT&T will rely primarily on natural attrition - employees retiring, taking other jobs, etc. - to accomplish those reductions."